Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. Rating of a domestic refrigerator is of the order of

10 tons

0.1 ton

5 tons

40 tons

2. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

0.2

1.2

3. In a refrigeration system, heat absorbed in comparison to heat rejected is

Same

More for small capacity and less for high capacity

Less

4. The freezing point of sulphur dioxide is

-75.2°C

-77.7°C

-135.8°C

-56.6°C

5. The minimum temperature to which water can be cooled in a cooling tower is

Ambient air temperature

Wet bulb temperature of air

Dew point temperature of air

Dry bulb temperature of air

6. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

1.25

2.15

5.12

7. The vapour compression refrigerator employs the following cycle

Carnot

Reversed Carnot

Rankine

Reversed Rankine

8. Most thermostatic expansion valves are set for a superheat of

20°C

15°C

5°C

10°C

9. The value of C.O.P in vapour compression cycle is usually

Always less than unity

Equal to unity

Always more than unity

Any one of the above

10. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

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11. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Detect liquid in vapour

Superheat the vapour

Collect liquid refrigerant and prevent it from going to compressor

Collect vapours

12. The domestic refrigerator uses following type of compressor

Axial

Miniature sealed unit

Centrifugal

Piston type reciprocating

13. Highest temperature encountered in refrigeration cycle should be

Much below critical temperature

At critical Temperature

Above critical temperature

Near critical temperature of refrigerant

14. Which of the following cycles uses air as the refrigerant?

Stirling

Carnot

Ericson

Bell Coleman

15. The condition of refrigerant after passing through the condenser in a vapour compression system is

Saturated liquid

Wet vapour

Superheated vapour

Dry saturated vapour

16. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.6

0.67

0.376

0.4

17. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

3.33

4.33

1.33

2.33

18. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 9

9: 1

1: 3

1: 1

19. In a refrigeration system, the expansion device is connected between the

Evaporator and compressor

Condenser and receiver

Receiver and evaporator

Compressor and condenser

20. Which of the following is not a desirable property of a refrigerant?

Large latent heat

High risibility with oil

Low boiling point

Good electrical conductor

Page 3 of 4

21. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

Zero

None of these

Negative

Positive

22. A thermostatic expansion valve in a refrigeration system

None of the above

Ensures the evaporator completely filled with refrigerant of the load

Maintains different temperatures in evaporator in proportion to load

Is suitable only for constant load systems

23. The curved lines on a psychrometric chart indicates

Dry bulb temperature

Relative humidity

Dew point temperature

Wet bulb temperature

24. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

T₂/ (T₂ - T₁)

(T₁ - T₂)/T₁

T₁ / (T₂ - T₁)

(T₂ - T₁)/T₁

25. The operating pressure for refrigerating units using R-12 as a refrigerant is

8 bar

15 bar

30 bar

2 bar

26. The boiling point of ammonia is

-30°C

-77.7°C

-33.3°C

-10.5°C

27. The capillary tube, as an expansion device, is used in

Room air conditioners

All of these

Domestic refrigerators

Water coolers

28. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(A) Heat dissipated to the surroundings

(B) Heat stored in the human body

(D) Difference of (A) and (B)

29. In a lithium bromide absorption refrigeration system

Ammonia is used as a refrigerant and lithium bromide as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

None of these

Lithium bromide is used as a refrigerant and water as an absorbent

30. A bootstrap air cooling system has

Two heat exchangers

Three heat exchangers

One heat exchanger

Four heat exchangers

Page 4 of 4

31. The bank of tubes at the back of domestic refrigerator is

Capillary tubes

Evaporator tubes

Refrigerant cooling tubes

Condenser tubes

32. Critical temperature is the temperature above which

A gas will never liquefy

Water will never evaporate

A gas will immediately liquefy

Water will evaporate

33. Which of the following statement is correct?

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

(B) The increase in air movement increases the evaporation from the human body.

(D) Both (A) and (B)

34. Freon group of refrigerants are

Nontoxic and non-inflammable

Non-inflammable and toxic

Inflammable

Toxic

35. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant entropy

Involves no change in volume

Takes place at constant temperature

Takes place at constant pressure

36. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Brine

Carbon dioxide

Freon

Ammonia

37. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

Super-cooling

Normal cooling

Sub-cooling or under-cooling

None of these

38. For obtaining high COP, the pressure range of compressor should be

Optimum

Any value

High

Low

39. Cooling water is required for following equipment in ammonia absorption plant

Condenser

Condenser, absorber and separator (rectifier)

Absorber

Evaporator

40. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Less

Unpredictable

Equally

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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